1. Field of the Invention
The present invention relates to a driving control device for a motor having a plurality of multi-phase coils for generating a rotating magnetic field to cause a rotor to rotate.
2. Description of the Related Art
Conventional AC motors, such as permanent magnetic motors and induction motors, use a stator coil to form a rotating magnetic field to thereby cause the rotor to rotate. Such AC motors use an inverter to control a stator coil current, and thereby can advantageously achieve control of an output torque over a wide range, as well as collection of a regenerative power in a battery.
The most common example of such an AC motor may be a three-phase motor having a three-phase coil with three phases displaced by 120 degrees from one another. Some systems, such as a system for driving two or more three-phase motors, may have two or more three-phase coils, and some motors having two or more three-phase coils for a single rotor may also have two or more three-phase coils in a single system.
In such a motor, each three-phase coil is provided with an inverter, and driving of the motor is controlled by controlling switching of the respective inverters. For this purpose, respective three-phase coil currents should be separately measured so that switching of the inverters are controlled based on the measurement result. In general, coil currents of two phases out of the three phases are measured for calculation of the three-phase coils, and inverter switching is controlled such that coil currents of the respective phases have desired values.
Therefore, in the case of a motor having a six-phase coil, four or more current sensors are required, which must be accurate sensors in order to precisely control the AC motor. As such a large number of current sensors are required, a resultant system is inevitably expensive.
It should be noted that a motor with an observer applied thereto is disclosed, for example, in Japanese Patent Laid-open Publication Nos. Hei 10-225199 and 2000-309697.